Digital-to-analog converter

Abstract

A converter for converting a series of digital input bits to an analog output employs a direct current comparator having a magnetic core and primary and secondary ratio windings coupled with the core. The primary winding is divided into two sections. A first group of the more significant input bits varies the number of turns of the first primary section which is traversed by a first direct current. A second group of less significant input bits varies the number of turns of the second primary section traversed by a second direct current. A direct current is also passed through the secondary winding, this secondary current being varied proportionally with the number of turns of the first primary section traversed by the first primary current. Modulation-detection windings arranged inside the core (which also acts as a magnetic shield) detect any net ampere-turns unbalance of the primary and secondary currents in the ratio windings. Detection of such an unbalance further varies the secondary current to tend to bring the unbalance to zero. The analog output is proportional to the secondary current. The splitting of the primary winding into two sections enables the converter to handle a larger number of bits, e.g. 20, than would be possible with a prior art type of primary winding, without the number of turns becoming unmanageably large.